1. Field
Embodiments of the present invention relate to a semiconductor device and a method of manufacturing the semiconductor device that is a semiconductor module having a case-less construction, for example.
2. Description of Related Art
FIG. 10 is a schematic sectional view of a part of a conventional semiconductor module 500 having a terminal case 61. This semiconductor module can be referred to as a semiconductor device having a case construction.
The semiconductor module 500, which is a general insulated gate bipolar transistor (IGBT) power module, includes semiconductor chips 57 such as an IGBT chip and a diode chip mounted on an insulated circuit board 51 with a conducting pattern.
The insulated circuit board 51 with a conducting pattern includes a ceramics 52 and metal foils adhered onto the upper and lower surfaces of the ceramics 52. The lower metal foil 53, which is a conductive layer, is joined to a metal base plate 56 with a solder 55a. The metal foil 54, which is a conducting pattern layer, on the upper surface of the ceramics 52 is adhered to the semiconductor chip 57 with a solder 55b. A terminal case 61 is adhered to the peripheral region of the metal base plate 56 with an adhesive.
The terminal case 61 has an externally leading out terminal 58, which is an externally leading out metal terminal, insert-molded. The externally leading out terminal 58 is connected to the semiconductor chip 57 through a bonding wire 59a. Then, the terminal case 61 is filled with silicone gel 60 and closed with a lid 62 at the top of the terminal case to complete the semiconductor module 500. The lid 62 is made of the same resin as that of the terminal case 61. The terminal case 61 is an outer frame made of a resin and holding the inserted externally leading out terminal 58.
Patent Document 2 discloses a semiconductor module having silicone gel filling a terminal case and epoxy resin thereon covering the terminal case. Patent Document 4 and Non-patent Document 1 disclose a semiconductor module having epoxy resin filling a terminal case but without a lid covering the terminal case.
The terminal case 61 is most often formed of a thermoplastic resin such as polyphenylene sulfide (PPS). For insulation protection against creeping discharge along the ceramic insulated circuit board 51 and for insulation protection of the semiconductor chip 57, the terminal case 61 is generally filled with silicone gel 60 or epoxy resin.
In order to ensure high temperature continuous operation of onboard IGBT power modules that need high temperature continuous operation, power cycle life needs to be elongated.
For elongating the power cycle life, epoxy resin exhibiting a high elastic modulus is more advantageous than silicone gel exhibiting a low elastic modulus. A high elastic modulus helps firmly hold solder joints and bonding wire joints and relaxes the stress on the joints caused by the difference in linear expansion of the components in the power cycle operation.
Examples of semiconductor modules with a case-less construction having no terminal case are disclosed in Patent Document 1 and Patent Document 2 that disclose semiconductor modules of a mold structure.
Patent Documents 1, 2, and 3 also disclose the use of transfer molding and compression molding for sealing a semiconductor module.
Patent Document 2 also discloses the use of a base plate and a frame jig for manufacturing a semiconductor module with a case-less construction in diversified, small-lot production.
[Patent Document 1]
Japanese Patent No. 3390661 (FIG. 1 in particular)
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 2011-238803 (FIG. 18 in particular)
[Patent Document 3]
Japanese domestic re-publication of PCT international application corresponding to international publication WO2005/004563
[Patent Document 4]
Japanese Unexamined Patent Application Publication No. H06-005742
[Non-Patent Document 1]
Fuji Electric Technical Journal 2012, vol. 85, no. 6, pages 430-434 (in Japanese)
In the semiconductor module with a terminal case structure disclosed in Non-patent Document 1 and Patent Document 4, sealing epoxy resin adheres to the terminal case with high strength when it hardens.
When the terminal case is formed of polyphenylene sulfide (PPS) resin, the PPS resin directly affects the sealing epoxy resin due to anisotropy of glass fibers in the PPS resin and the crystallization temperature, Tg=90° C.-130° C.
As a result, large internal stress is generated in the semiconductor module and hinders elongation of power cycle life of the semiconductor module, hardly achieving high reliability.
A means to solve this problem is sealing the semiconductor chip with epoxy resin by means of transfer molding or compression molding without using a terminal case. This method of manufacturing a semiconductor module having case-less construction, however, needs expensive molding equipment and a metallic mold, and thus requires high equipment investment costs. Because diversified, small-lot production of semiconductor modules needs various types of expensive metal molds, this manufacturing method is not suited to diversified, small-loot production.
The semiconductor modules with a case-less construction disclosed in Patent Document 1 and Patent Document 2 are manufactured by means of transfer molding, and the semiconductor module disclosed in Patent Document 3 is manufactured by means of compression molding. Both these molding techniques need very expensive molding equipment and metallic mold, at a cost of several tens to one hundred million yen, and are not suited to diversified, small-lot production.
The method proposed in Patent Document 2, though suited to diversified, small-lot production, needs a large number of parts and takes a lot of labor for assembling, dismantling, and cleaning of jigs, raising the manufacturing costs.
All of Patent Documents 1 through 4 and Non-patent Document 1 fail to disclose a method of manufacturing a semiconductor module with a case-less construction that use neither transfer molding nor compression molding.